1. Field of the Invention
The present invention relates to a transmitter for coding error correction codes and the receiver for decoding error correction codes on a transmission frame which transmits data in the units of cells (packets) in Asynchronous Transfer Mode. The Asynchronous Transfer Mode may especially generate burst errors caused by cell loss, adding to random errors.
2. Description of the Related Art
Conventionally, the transmitter and receiver for coding error correction codes in which random errors and burst errors may occur uses interleave methods. Symbols are set in two directions, which are the direction of transmission, and the orthogonal direction of transmission: Error correction codes are generated in the orthogonal direction of transmission.
FIG. 44 shows a transmission frame composed of cells which applies interleave methods. The interleave methods are described in page 220 "Hugo-riron (Code Theory)" written by Hideki Imai published by The Institute of Electronics Information and a Communication Engineers (Heisei 2).
L data cells 1 are composed of N data symbols, in FIG. 44. K check cells 2 are composed of N check symbols. The transmission frame has L data cells and K check cells. The transmission frame comprising (L+K) cells uses interleave method. Input data are set from point A in the upper left of the transmission frame to B, are set at C point in the direction of numeral 3, and ends at D point in the right.
The operation is explained as follows. In FIG. 44, error correction coding is carried out from L symbols in every data cell to the orthogonal direction of transmission, that is, the horizontal direction (the X direction in FIG. 44). Then, K check symbols are generated and stored in K check cells 2. The transmission frame is transmitted in cell units in the Y direction (the vertical direction), in FIG. 44. Assuming that error correction codes are Reed Solomon codes having a frame length for error correction of (L+k) symbols and K check symbols, errors of K/2 symbols (Omit fractions) can be corrected in the X direction. A maximum loss of K cells caused by transmission noise or congestion of network can be decoded, if the location of the lost data cells is identified.
The transmission frame includes data in an information field 42 between an information header 41 and an information trailer 43 as shown in FIG. 43. Problems to be Solved by the Invention
As has been described in the related art, the conventional transmission frame composed of cells uses interleave methods in units of symbols for the error correcting coding. In order to correct errors effectively, it is necessary to set the length of (L+k) symbols for the transmission frame relatively long and transmit the frame after data of L cells is buffered. Decoding is carried out after all (L+k) cells are received. Therefore, in case slow-speed transmission is performed, the conventional art contains the problem of transmission delay being increased
In addition, it has also no way of finding the location of the cell loss. It has also insufficient efficiency in coding because coding is done symbol by symbol.
The present invention is done so as to solve the foregoing problems. The transmission frame is transmitted before all (L+K) cells are buffered. In the present invention, transmission has started at an early stage. Then it maintains an effective error correcting ability for both random errors and burst errors caused by cell loss. And, it is an object of the present invention to provide an apparatus which can detect the location of cell loss easily, and has an effective error correcting ability.